I encouraged XBC early in the other thread for the sake of variety, but since reading the rest of it, and having revisited the fact that XBC basically sold out to M$, and finally that Xlink already has an API for devs to implement in thier dash, I vote Xlink.
Xlink has more players anyway. I mean, who doesn't have XBMC??? Sides, the n00bs who use Xlink make excellent targets in Halo2...